The medial and lateral menisci are a pair of cartilaginous structures in the knee joint which together act as a crucial stabilizer, a mechanism for force distribution, and a lubricant in the area of contact between the tibia and femur. Without the menisci, stress concentration occurs in the knee in conjunction with abnormal joint mechanics, and premature development of arthritic changes occurs.
In the prior art, treatment of injured or diseased menisci has generally been both by surgical repair and by excision. With excision, regeneration of meniscal tissue may occur. Additionally, it is known that meniscal fibrochondrocytes have the ability to migrate into a defect filled with a fibrin clot and form tissue apparently similar to normal meniscal fibrocartilage. When an adequate matrix scaffold is present within a meniscal defect, such meniscal fibrocartilage may be formed. Meniscal tissue is also capable of self-repair when exposed to bleeding tissues, and additionally, it is also known in the prior art that meniscal cells in tissue culture are capable of cell division and matrix synthesis. Replacement of an injured meniscus in an otherwise healthy joint may prevent arthritic changes and may stabilize the joint. In diseased joints, replacement of the meniscus may reduce the progression of the disease process, and may provide pain relief. Allografting or meniscal transplantation, is one method of replacement which has been executed both in dogs and in humans. However, this approach has been only partially successful over the long term due to the host's immunologic response to the graft, to failures in the cryopreservation process, and to failures of the attachment sites.
In alternative prior art replacement approaches, menisci have been replaced with prostheses composed of permanent artificial materials. Such prosthesis have been constructed of purely artificial materials in order to minimize the possibility of an immunological response. In addition, the use of such materials is believed to be advantageous because it permits construction of a structure which can withstand the high and repeated loads which are encountered in the knee joint, and because it can alter the joint mechanics in beneficial ways that biological materials would not tolerate.
For example, a Teflon net has been used to replace the resected meniscus of a dog upon which fibrous ingrowth or regeneration was observed, although accompanied by significant chondral abrasion. A prosthetic meniscus has also been constructed from resilient materials such as silicone rubber or Teflon with reinforcing materials of stainless steel or nylon strands (U.S. Pat. No. 4,502,161). A meniscal component has also been made from resilient plastic materials (U.S. Pat. No. 4,085,466). In addition, reconstruction of meniscal lesions has been attempted with carbon-fiber-polyurethane-poly (L-lactide), but its success with these materials is minimal (Leeslag et al., Biological and Biomechanical Performance of Biomaterials (Christel et al., eds.) Elsevier Science Publishers B.V., Amsterdam. 1986, pp: 347-352).
However, the replacement of meniscal tissue with structures consisting of permanent artificial materials generally has been unsuccessful, principally because the opposing articular cartilage of human and animal joints is fragile. The articular cartilage in the knee will not withstand abrasive interfaces, nor compliance variances from normal, which eventually results from the implantation of prior art artificial menisci. Additionally, joint forces are multiples of body weight which, in the case of the knee and hip, are typically encountered over a million cycles per year. Thus far, prior art permanent artificial menisci have not been composed of materials having natural meniscal properties, nor have they been able to be positioned securely enough to withstand such routine forces.
Therefore, what is needed is an improved prosthetic meniscus composed of biocompatible materials which are soft and lubricating.
Repair of other tissues such as skin and nerve has been attempted using both synthetic and natural materials. For example, Yannas et al., fashioned endodermal implants, and artificial epidermis out of natural collagen and glycosaminoglycans (U.S. Pat. No. 4,060,081). Nyiles et al. (Trans. Am. Soc. Artif. Intern. Organs (1983) 29:307-312) reported the use of synthetic resorbable polyesters for peripheral nerve regeneration applications, and the use of collagen conduits as a scaffold for nerve regeneration.
However, even with the foregoing technologies which have been applied to the reconstruction of anatomical structures other than knee joints, a structure suitable as a prosthetic meniscus and constructed from totally resorbable natural materials, or analogs thereof, has not been developed in the prior art.
Accordingly, it is an object of this invention to provide an improved meniscal prosthesis which allows for normal joint motion.
Another object is to provide a meniscal replacement or prosthesis which is biomechanically able to withstand normal joint forces and is able to function at those loads to protect the cartilage and stabilize the joint.
Yet another object is to provide a resorbable meniscal prosthesis which acts as a temporary in vivo scaffold for meniscal fibrocartilage infiltration and regeneration.
Still another object is to provide a meniscal prosthesis which is composed of biocompatible materials having an organization equivalent to that of the normal meniscus.
A further object is to provide a meniscal prosthesis which is adapted for implantation by standard operative techniques.
Another object is to provide a method of regenerating meniscal tissue in vivo.
Still a further object is to provide a method by which such prosthetic menisci can be fabricated.